Process and apparatus for continuous filtration



Aug. 30, 1932. F. w. HALL 1,874,972

PROCESS AND APPARATUS FOR CONTINUOUS FILTRATION Filed Nov. 4, 1929 2 sheets-sheet '1 FIG.1;

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F. w. HALL 1,814,372 PROCESS AND APPARATUS FOR CONTINUOUS FILTRATION Filed New--41 1929 2 Sheets-Sheet 2 FIG.2.

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- lii into a plurality Patented Aug. 30, 1932 NITED STATES vPATENT opt-reg FRANK W. HALL, PORT ARTHUR, TEXAS, ASSIGNOR TO THE TEXAS COMPANY; OF

.NEW YORK, N.-

Y., A CORPORATION OF DELAWARE PROCESS AND APPARATUS FOR CONTINUOUS FILTRATION Application filed November 4,1929. Serial No. 464,534.

This invention relates to improvements in iprocess of a nd apparatus for the continuous ltration of solid materials from liquids or for'the continuous filtration of solids from liquids in the presence of comminuted filteraid material and may be particularly adapted to the filtration of petroleum oils such as the filtration of sus ended wax constituents from hydrocarbon oil:

In its general ap lication the invention comprises a process of and apparatus for continuous filtration wherein one or more tering elements, which in the preferred embodiment briefly cons sts of rotating discs divided flat sides of which are covered with a suitable fabric, eachrsection having a separate con P duit all of which terminate in a multi-chambered core or shaft, each conduits termina- 29 tion forming means ofattaching a disc section to said shaft. Thesections are passed by rotation through successive zones of filtration, cake washing and drying, cake removal, reverse tially cake free cyclicrepetition of the steps in this order. 3

During passage of the sections of the filtering. elements through the filtration zone 1i uid is drawn through the surfaces leaving so id deposits thereon in the form of a cake. As each section is passed through the cake washing and drying zone where suction is still taken on the elements, the outer surface of the cake is sprayed with a suitable solvent or washing-fluid which dissolves or displaces particles of filtrate remaining on thesurface of, or in,'the cake and which may be, for the most part, drawn through the cake by the continuin suction taken on the filtering elements uring an appropriate intervalof time. As the different sections of the filtering elements are passed through the zone of cake removal a blow-backor back pressure is applied through the individual conduits to the inside of the filtering surfaces which tends to distend or inflate the fabric and dislodge the cake from-the o posite side thereof and while applying this ack gfessure the cake is removed. FoIlowing t e cake removal step the sections whose surfaces are relatively clean of sector-like sections, the

flow washing of the substanfiltering surface and so on in matically.

"ed byX and- ,the supply pipe forand source are passed through the reverse flow washing zone where an appropriate solvent or washing fluid, which may be aportion of the filtrate if desired, is delivered underpressure and preferably in the form of a spray or mist to the inside of the filtering surfaces to thoroughly cleanse and wash the said surfaces.

Thus a foremost object of this invention is to carry on a continuous filtering process in which a desirable material is properly filtered at the highest rate attainable.

Another object of the invention is to effectively cleanse the filtering surfaces repeatedl without ceasing operation.

gtill another object of the invention is to provide suitable means for carrying on the rocess.

The foregoing objects of the invention, together withothers which will be apparent, may be better, understood from the following description taken in connection with the drawings illustrating a preferred apparatus forpracticing the present process in which:

Figure 1 is a view in cross section through a filter showing a filtering element in full ele- 7 vation and the piping, pumps, etc. diagrajifi I Figure 2 is a fragmentary view of thehollow haft and a filtering element taken on the section 2-2 of Figure 1 showing the valve in 30 full and its functional relationship to the various sections of the filtering elements. As shown in Figure 1, one or more disc-like filtering elements or leaves 8, composed of a. number of sector-like sections 9a, 9?), etc., are 35 mounted on a hollow shaft 12. u The hollow shaft 12 with the attached elements 8 is caused to rotate in a counterclockwise direction, by

suitable means not shown, so that the sections composing the filtering elementsare there-v by passed through a bowl 14 in which an admixture of liquidand solids to beyfiltered is maintained, referably at the levelindicatof which are not shown. g 1

The sections9a, 96, etc., consistin of suitable frames are covered with suita 1e filter fabric, accordin toconventional methods construction. ach section of the filtering elements is connected separately by means of, I00

a conduit 10a, or 10?), etc., to corresponding conduits 31a, 31?), etc., in the wall of the hollow shaft 12 and in operation functions en-.

tirely independent of the remaining sections.

The filter valve 11, which-will be fully described later herein when discussing the parts illustrated in Figure 2, is centrally located at one end of the hollow shaft 12. By meansof "17a, and with meansfor supplying a spra or mist reverse flow or backwash fluid, whic will be fully described presently, through a pipe 16.

A suction line 1 from the tank 6 to a pump 2 and a discharge line 3 from the pump 2 to a suitable spray 4 serves to conduct washing liquid from storage and delivers it to the surface of the cake when the filtering sections are passed through the cake washing and drying A vacuum pump 21 serves to maintain-the pressure in tanks 6 and 7 below atmospheric,

while the filter is being operated, and accordingly filtrate is drawn through thefiltering lution of t e bulk of the filtrate with was elements as the sections are passed through the filtering zones, and is conducted through the pipe 18 into the tank 19, while the washing liquid plus dislodged or dissolved parti-' cles of filtrate and air or gas is drawn through the filter element as the sections are passed through the cake washing and drying zone and conducted through the pipe 5a to the tank 6.

More complete extraction of the remaining particles of liquid is efi'ected by contin ulng to exert vacuum on each particular section for a short time after the adhering cake has passed beyond the range of the washing sprays.

I 'Since the washing liquid passing through thecake contains some filtrate liquid and since a large amount of air or as is also drawn through the cake during this washin the additional storage tank fi is rovide p rate stora tanks thus avoi unnecessa tion during its passage through the cake washing and drying zone, valves 7a and 20a may be adjusted to maintain a differential in vacuum between tank 19 and .tank 6 so that the flow of air or gas throughithe cake on the surface of any one section" after emerging from the filtering mixture does not cause appreciable variation in the vacuum being maintained on tank 19.

The means for supplying the spray reverse flow or backwash comprises an air or flue gas supply line 23 from a source (not shown),

provided .with a valve 24 leading to one inlet connection of a mixing nozzle 22, and a backwash liquid supply line 25 (from a source not shown), provided with a valve 26 leading to the other inletconnection of the nozzle 22 which has an outlet pipe 16 as previously mentioned. Suitable pressure gauges 27 28 and 29 are provided in the lines 23, 25, and 16, as shown.

Referring now to Figure 2, the tapering stationary filter valve 11 is seated in an end of the shaft 12. Within the filter valve 11 are four separate ports 33, 34, '35, and 36. The spread'of these ports is illustrated by the sector-type areas labeled filtration, cake washing and drying, blow-back and cake removal and reverse flow back wash, in Figure 1, and in the circle which they form occupy a proximately 160, 40, and 40 thereo respectively, the remaining 30 of the circle being occupied by the walls or partitions between the ports. The port 33 is directly connected with the filtrate tank 19 through the pipe 18; the port 34 is directly connected to the cake wash, liquid tank 6 through the pipe 5; the

port 35 is directly connected to a source of supply of low ressure gas or air (not shown) by means of t e pipe 17; and the port 36 is directly connected to the system for supplying the solvent or spray as a'rever se flow wash throu h the pipe 16.

During t e counterclockwise rotation of the shaft 12 the ports 32a, 326, etc., formed at the ends of the conduits 31a, 31?), etc., by the tapering seat in the end of the shaft 12 for the valve 11, register successively with the filter valve ports 33, 34, 35 and 36 for appropriate intervals of time to provide the proper conditions of vacuum filtration, cake was ing, cake discharge, and reverse flow or backwash to the individual sections 9a, 95, etc., of the filterin disc 8 in accordance with the position of eac section in the cycle.

In certain filtering operations such as the dewaxing of hydrocarbon oils it is'preferable to omit the step of washing the cake by application of a wash liquid in the form of a spray against the outer surface thereof. The exertlon of vacuum is continued, however, throughout what corresponds to the whole period of this washing zone thereby drying the cake and removing the small amount of filtrate that might otherwise remain therein.

In a preferred embodiment of the invention particularly adapted to the dewaxing of a hydrocarbon oil, the wax-bearing oil,

preferably cut back or diluted with a suitable solvent which may petroleum naphtha, having admixed therewith a comminuted fil-' tion of the filter disc 8 he stationar ter-aid material, is chilled to the proper temperature and continuously fed into the bowl 14 by means not shown,'and maintained at sufficient depth in the bowl, as indicated by the dotted lines at X and Y so that the filter sections 9a, 96, etc., are submerged as they rotate through the bowl 14.

As each individual section 9a, 96, etc., is submerged in the admixture of oil, wax and filter-aid material contained within the bowl 14 the corresponding ports 32a, 32?), etc., in the tapered valve seat of the hollow shaft 12 register with the valve 11 through whic the particular seeis directly connected through the pipe 18 to tank 19 which is maintained under vacuum by means of the vacuum pump 21 as previously discussed. In response to the vacuum thereby exerted on the inner side of the filter section the liquid is drawn through the filter fabric leaving the solid materials deposited upon the outer surface thereof. The port 33 valve .11 will embrace as ny as five o the ports 32a, 321), etc. in the shaft 12, due to its spread as previously explained, throughout approximately v160 of the 360 cycle.

As a section of the filtering element, e. g. 10a, is moved out of the body of the filtering mixture the corresponding port 324; leaves the port 33 and begins to register with the port 34 which has a spread of approximately 90 of'the 360 cycle. Durin this period vacuum is still exerted, lprefers. ly to a lesser degree than that in t e period in which the port 32a re 'sters with the port 33, on the inner side b the filtering surface of section 10a thereby tending to remove the last traces of filtrate remaining in the conglomerate of waxyv constituents and filter-aid mate- I rials comprising the built up cake on the outer surface of the filter element.

Upon further rotation of the shaft 12 the filter sections carrying the vacuum dried cake are moved into the zone of cake discharge throughout which zone Hie ports 32a, 3%, etc., register with the port 35 which has a spread of approximately wherein a blast of relatively low pressure air or flue gas is applied to the inner s1de of the filter sections.

In this way the filter fabricis caused to bulge outwards, loosening or dislodging the cake to facilitate its removal by scrapers or other suitable means, not shown in the drawings, whereby the cake is, prevented from falling back into the filter bowl 14 and may be deliv ered to a bin or other receptacle. As has been previously discussed the substantially dry cake contains waxy constituents and is preferably removed and conveyed awayfrom the filtento a recovenysystem where the waxy constituents-are separated from the filterid material and recovered and the filter-aid maing 40, approxlmately,

ort 33 of the filter the filtrate storage terial is conditioned for reuse in further dewaxing and filtering operations.

As the rotation of the shaft 12 is continued the filtersections are assed out of the zone of dischar e and arch fabric wasiing zone comprising the remainof the 360. cycle. Throughout the reverse flow filter fabric washing-zone the ports 32a, 32?), etc., register with the port 36 thereby forming a passage through which the solvent backwash fluid, preferably a portion of the filtrate oil itself rought into the filter' in the form of a spray, is introduced to the interior of the filter section, and forced through the filter fabric in a reverse direction to that followed by the filtratein the zone of filtration. Leaving this reverse flow washing zone the filter sections are again passed into the filtering portion of the cycle and the foregoing steps are cyclically repeated in the same order,

Thus by washing the filter fabric in the manner above described a high rate of filtra-f tion is maintained and the necessity for frequent shut-downs for cleaning is avoided thereby greatly increasing the operating time.

- Reverse flow washing the fabric with fil-' trate oil after thecake has been completely removed therefrom rather than during the step of actually removingthe cake avoids the possibility of a portion of said filtrate oil, which has penerated the fabric, again mixing with the cake being discharged and therefore resulting in a loss of valuable dewaxed oil in the cake being removed from the system.

It' is preferable to apply the backwash or,

solvent o1l the form of a spray or suspension in a gas since under these conditions penetration of the fabric .by the filtrate oil or other solvent wash in a direction reverse to that atwhich the filtrate flowed through it in the filtration zone may be more effectively accomplished. 1

That ortion of the filtrate oil used as a reverse ow wash for the filter fabric and which actually penetrates the filter fabric trickles down into the bowl of the filter where it commin les with the admixture of suspended wax fi ter-aid material and unfiltered oil which has been diluted with naphtha or other suitable solvent preparatory to filtration.

Thus by employing the filtrate oil rather than naphtha on "some other solvent as a wash liqthe further undesirable dilution of the filtering mixture can be avoided. While the filtrate oil itself is preferred as a wash, the employment of a na htha or'other solvent wash 'is notapreclude and can be taken advantage of without undue dilution of the filtering mixture since washing-of the filtering surface is effected witha minimum volume of- 1 liquid whensuch washing performed after the cake ha's'bi5e discharged as practiced in this invention.-;;; v v

Many, modifications andivariations of the invention may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

M What I claim is:

' 1. A process of dewaxing hydrocarbon oils which comprises continuously charging a mixture of oil, precipitated wax and com minuted filter aid material to a filtering zone b wherein a plurality of revolving filtering surfaces pass alternately through zones of positive pressure filtration andcake drying and reverse pressure cake discharge and filter surface washing depositing solids in the form'of 5 a compact cake on the one side of the filtering surfaces while inthe zone of positive pressure filtrationpcontinuing to apply positive pressure while in the drying zone to remove traces of oil from the cake, applying a back go pressure of an incondensable as to the reverse side of the filtering sur aces while in the cake discharge zone to loosen the cage, removing the dislodged cake, continuing 0 apply said gaseous back pressure uniformly over the entire reverse side of the filtering surfaces after removal of the filter cake -there I from and during passage through the filter surface washing zone and simultaneously spraying petroleum naphtha in the form of a finely separated mist against the reverse I side of the filtering surfaces into which it is forced by the gas to remove wax con tituents from the pores to produce substan 'ally clean filter surfaces prior to the entrance of said surfaces to the zone of positive pressure filtration, and collecting a dewaxed oil from the system,

2. A process of dewaxing hydrocarbon oils which comprises continuously char ing a 40 mixture of oil, precipitated wax and comminuted filter aid material to a filtering zone wherein a plurality of revolving filtering surfaces pass alternately through zones of positive pressure filtration and cake (1 ing and reverse pressure cake discharge and lter surface washing, depositing solids in the form of a com act cake on the one side of the filtering sur aces while in the zone of ositive pressure filtration continuing to app y positive pressure while in the drying zone toremove traces of oil from the cake, applying a back pressure of an incondensable gas to the reverse side of the filtering surfaces while in the cake discharge zone to loosen the cake,

- removing the dislodged cake, continuing to applyssaid gaseous back ressure uniformly over theentire reverse s1de of the filtering surfaces after removal of the filter cake therefrom and during passage through the filter to surface washing zone and simultaneously spraying a portion of filtered dewaxed oil in the form of a finely separated mist against the reverse side of thefiltering surfaces into which it is forced by the gas to remove waxy 06' constituentsfrom the pores to produce substantially clean filter surfaces prior to the en-. trance of said surfaces to the zone of ositive pressure filtration, and collecting a d waxed oil from the system.

3. A process of separating waxy constituents from hydrocarbon oils whichcomprises maintaining a body of chilled hydrocarbon oil and precipitated wax in a filtering zone,

revolving through said body a series of partially immerged disc members, each contain- 76 ing a plurality of bag-like filtering surfaces, passing saidfiltering surfaces during each revolution successively through zones of filtration, cake drying, cake discharge and reverse flow washing of the filter fabric, apply- 1 80. ing a vacuum to the interior of said filtering surfaces when entering the zone offiltration whereby the waxy constituents are deposited upon the exterior of said surfaces in the form 0 a compact filter cake and a dewaxed oil is passed to the interior thereof, continuing to apply vacuum to the interior of said surfaces while in the cake drying zone to remove traces of oil and dry the cake, releasing the vacuum as the filtering surfaces enter the zone ofcake discharge and applying a back pressure of an incondensable gas to the interior thereof to loosen the cake, removing the dislodged cake, passing the filtering surfaces through a reverse flow washing zone after removal of the cake while continuing to apply said gaseous back pressure uniformly over the whole interior thereof during passage through said washing zone and simultaneously spraying an oil solvent in the form of a mist into said gas to force said mist against the interior of the filtering surfaces to dissolve waxy constituents from the'pores and produce substantially clean filtering surfaces prior to the entrance of said filtermg surfaces to the zone of filtration, and collecting a dewaxed oil from the system. I

4. In a rotary suction filter for se arating solids from liquids, a plurality of lter elements radially mounted around a central shaft, said shaft being provided with conduits communicating with said filter elements, a valve containing suitable ports centered at one end of said shaft, a filtrate line,

a filter cake wash liquid line, a reverse pressure gas line, and a reverse flow filter fabric washing fluid line connected to individual ports 'in said valve,,means for applyinga vacuum to the filtrate and filter cake wash liquid lines, means for mixing and 1ntroduc-' ing a solvent in theform of a mist suspended in gas to said reverse fiow filter fabric washing fluid line, the entire arrangement bemg such that when the shaft is rotated, the conduits therein register with the ports in said ,valve so .that the filter elements communicate *successively'with the vacuum filtrate line to produce filtration and deposition of sohds on the filter elements, with the vacuum filter cake wash liquid line to draw a washing 

